] .1 fir ir nil ural Ohemistry. 



DEFINITIONS. 



It now becomes necessary to define, in a fragmentary way, 

 some of the commoner terms used in chemistry. 



Acid. A substance generally possessing a sour taste and the 

 property of changing vegetable blues, as blue litmus, to red. As 

 types of acids, we have sulphuric acid, commonly used for the 

 Babcock test, and acetic acid, the principal acid in vinegar. The 

 possession of a sour taste and the power of changing vegetable 

 blues to red is indicated by saying that the substance has an acid 

 reaction. 



Alkali. A substance opposed in its properties to an acid, cap- 

 able of neutralizing and destroying the characteristics of an acid, 

 forming in so doing, a salt. The most important alkalies are 

 soda, potash, lime, and ammonia. A substance is said to have an 

 alkaline reaction if it turns certain vegetable colors, as red litmus, 

 to a blue color. 



Organic matter, strictly speaking, is matter which has been 

 produced by organisms, such as plants or animals, but the term 

 is used in a wider sense in chemistry for any compound of carbon, 

 whether produced by life processes or artificially. Almost all 

 forms of organic matter, when strongly heated out of contact with 

 air, blacken, owing to the liberation of carbon. With free access 

 of air, combustion occurs, and carbon dioxide and other products 

 are formed. 



Oxidation and Reduction. By oxidation, literally speaking, 

 is meant union with oxygen, but in a chemical sense the term is 

 given a wider significance, that is, combination with more oxygen 

 or with some substance playing the part of oxygen. 



Reduction is used in exactly the opposite sense. A substance 

 , which brings about oxidation, is called an " oxidizing agent" 

 while one which removes oxygen is called a "reducing agent." 

 Common oxidizing agents are air, nitric acid, nitrates and chlor- 

 ine ; common reducing agents are easily oxidizable metals, as zinc, 

 and n mi iy forms of decaying organic matter. 



